Effects of Ge Co-Doping on P-Related Radiation-Induced Absorption in Er/Yb-Doped Optical Fibers for Space Applications

The natures of most radiation-induced point defects in amorphous silicon dioxide (a-SiO2) are well known on the basis of 56 years of electron spin resonance (ESR) and optical studies of pure and doped silica glass in bulk, thin-film, and fiber-optic forms. Many of the radiation-induced defects intrinsic to pure and B-, Al-, Ge-, and P-doped silicas are at least briefly described here and references are provided to allow the reader to learn still more about these, as well as some of those defects not mentioned. The metastable self-trapped holes (STHs), intrinsic to both doped and undoped silicas, are argued here to be responsible for most transient red/near-IR optical absorption bands induced in low-OH silica-based optical fibers by ionizing radiations at ambient temperatures. However, accelerated testing of a-SiO2-based optical devices slated for space applications must take into account the highly supralinear dependence on ionizing-dose-rate of the initial STH creation rate, which if not recognized would lead to false negatives. Fortunately, however, it is possible to permanently reduce the numbers of environmentally or operationally created STHs by long-term preirradiation at relatively low dose rates. Finally, emphasis is placed on the importance and utility of rigorously derived fractal-kinetic formalisms that facilitate reliable extrapolation of radiation-induced optical attenuations in silica-based photonics recorded as functions of dose rate backward into time domains unreachable in practical laboratory times and forward into dose-rate regimes for which there are no present-day laboratory sources.

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Theory of radiation-induced absorption in optical fibers

10.1117/12.177647 ◽

1994 ◽

Author(s):

Duncan T. Liu ◽

Alan R. Johnston

Keyword(s):

Optical Fibers ◽

Induced Absorption ◽

Radiation Induced

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Radiation-Hardened Optical Fibers for High Dosage Space Applications

MRS Proceedings ◽

10.1557/proc-244-3 ◽

1991 ◽

Vol 244 ◽

Cited By ~ 7

Author(s):

A. E. Miller ◽

M. F. Yan ◽

H. A. Watson ◽

K. T. Nelson

Keyword(s):

Optical Fibers ◽

Fiber Types ◽

Space Applications ◽

Broad Absorption Band ◽

Pure Silica ◽

Different Temperatures ◽

Operating Limits ◽

Radiation Hardened ◽

Radiation Induced ◽

Doped Fibers

ABSTRACTHydrogen doping of optical fibers has been examined as an approach to increase the radiation hardness of optical fibers for high dosage (107 rad) space applications. A systematic study has been performed on 4 types of optical fibers designed to operate at 1.31 and 1.55 μm and doped with up to 8200 ppm H2. For low dosages, the most significant reductions m radiation-induced losses were obtained with low H2 concentrations (<10 ppm). Spectral loss measurements for hydrogen-doped fibers containing GeO2 show a radiation-induced loss peak at 1.45 μm and a broad absorption band around 0.6–0.8 μm. These bands are not observed in the pure silica-core fibers.Fibers were fabricated to permanently trap 2.7 ppm H2 and the radiation-induced losses in these fibers are 35 to 85% that of the untreated fibers. Experimental data are used to delineate the γ-T-α operating limits which define the maximum gamma radiation (γ) dosages at different temperatures (T) while still meeting a requirement of α<150 dB/km. Among the four fiber types, hydrogen-doped silicacore fibers show the widest operating range and smallest radiation-induced loss for space applications. However, hydrogen-doped fibers with moderately high GeO2-doped core offer the best tradeoff between the bending and radiation-induced losses.

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